1. Field of the Invention
The present application is directed to a support structure for positioning an exothermic welding mold adjacent a surface to which an electrical grounding wire is to be welded. The support structure may be used for positioning other articles such as a pipe, angle iron, small beam, etc., adjacent a surface to which the article is to be welded.
2. Prior Art
Electrical grounding is important in all phases of modern electrical power system operations. At electrical sub-stations, grounding is of particular importance since they are sites of high concentration of electrical power and continuity of electrical service is manditory.
The electrical grounding of sub-stations serves the following purposes:
1. Protection against lightening and surge currents.
2. System grounding:
A. To stabilize current potentials with respect to ground. PA1 B. To provide a means of circuit relaying to clear ground faults.
In addition, it is important that electrical grounding be provided for normally non-current carrying structures and parts and for auxiliary low voltage circuits for the safety of personnel.
Low resistance and adequate current carrying capacity are important requirements for the electrical grounding of sub-stations. Also, low resistance is very important for electrical grounding protection against lightning and electrical surges so that the high current disturbances of short duration will pass quickly to the earth.
To ensure the proper electrical grounding, it is important that the conductor used between the ground rods and the equipment is of a sufficient cross-sectional area to prevent melting of the conductor during the period that the fault current flows. Even though the electrical grounding protective device is used for a short period of time, adequate grounding cables and the extra protection of welded connections is a small investment when considering the total cost of the station.
One method of connecting a ground wire to a metal framework has been through the use of a nut and bolt. A hole is drilled into the steel structure and a bolt is inserted therethrough. A nut is attached to the threaded portion of the bolt and the ground wire is looped adjacent the head portion of the bolt. By screwing the nut onto the threaded portion of the bolt, the ground cable is firmly affixed adjacent the steel structure. This method of connecting a ground wire to a steel structure has a number of drawbacks:
1. The nut has a tendency to loosen from the bolt with the result that the electrical grounding cable is not firmly affixed adjacent the steel structure or may be dislodged.
2. The bolts have a tendency to corrode with the result that the electrical grounding cable may become dislodged from the metal structure.
3. The bolts tend to have a different current carrying capacity than the electrical grounding conductors. Thus, bolts are not an ideal component of an electrical grounding system.
A preferred way of connecting an electrical grounding cable to a steel structure is by the use of an exothermic weld mold. One method of achieving this weld is by use of the CADWELD process, which employs a high temperature type graphite mold and an exothermic charge which includes a welding charge and the starting powder. A welded connection between the electrical grounding cable and the metal structure does not have a tendency to loosen or to corrode since no mechanical pressures or contact surfaces are involved. In addition, the welded material may be selected to have an equal current carrying capacity as that of the electrical grounding cable.
Although it is preferred that the electrical grounding cable be welded to the metal structure, it is sometimes extremely difficult especially when grounding large towers or the steel support structures of a large building for a single individual to employ an exothermic mold. It has been found that in many instances it is necessary for two employees to work as a team to position the exothermic mold adjacent the electrical grounding cable and the steel structure to produce the necessary welded connection. Utilizing two individuals to position the exothermic mold is both expensive and troublesome especially, as stated above, when dealing with tall towers and the steel support structures of large buildings.
In addition, it is sometimes difficult to position an article such as a pipe, angle iron or small beam adjacent a surface to which it is to be welded. As discussed above, the present invention may readily be utilized to position such an article adjacent a surface.